Measurement of B9Upsilon(5S) to Bs(*) Bs(*)bar Using phi Mesons

Abstract

Knowledge of the Bs decay fraction of the Y(5S) resonance, fs, is important for Bs meson studies at the Y(5S) energy. Using data collected by the CLEO III detector at CESR consisting of 0.423 1/fb on the Y(5S) resonance, 6.34 1/fb on the Y(4S) and 2.32 1/fb in the continuum below the Y(4S), we measure B(Y(5S)-> phi X)=(13.2+/- 0.7 ^{+2.2}_{-1.4})% and B(Y (4S)-> phi X)=(7.1 +/- 0.1 +/- 0.6)%, the ratio of the two rates is (1.9 +/- 0.1 ^{+0.3}_{-0.2}). This is the first measurement of the phi meson yield from the Y(5S). Using these rates, and a model dependent estimate of B(Bs -> phi X), we measure fs=(27.3 +/- 3.2 ^{+14.6}_{-~6.1})%. We update our previous, independent measurement of this branching fraction using the inclusive Ds yields to be (21.8 +/- 3.4 ^{+8.5}_{-4.2})%, due to changes in the $D_s^+ -> phi π^+$ branching fraction and a better estimate of the number of hadronic events. We also report the total Y(5S) hadronic cross section above continuum to be sigma(e^+e^- -> Y(5S))=(0.301 +/- 0.002 +/- 0.039) nb. This allows us to extract the fraction of B mesons as (58.9+/-10.0+/-9.2)%, equal to 1-fs. Averaging the three methods gives a model dependent result of fs=(26^{+7}_{-4})%.